Blasting cap



Nov. 24, 1953 A. J. BAROCCA ETAL BLASTING CAP Filed Aug. 19, 1949 FIG.

BAROCCA INVENTORSI FIG. 3.

- ALDO J.

F REDERlCK R. BYfldaa a SE VEY ATTORNEYS.

l atented Nov. 24, 1953 D STATES PATENT OFFICE BLASTING CAP Aldo J. Barocca,

Godfrey,

and Frederick R.

Seavey, Alton, Ill., assignors to 01in Industries, Inc., East Alton, 111., a corporation of Delaware Application August 19, 1949, Serial No. 111,132

1 Claim. 1

This invention relates to electric detonators and more particularly to a method of sealing the bridge plug into the mouth of an electric detonator to render the same waterproof and mechanically strong.

The electric blasting caps in general use heretofore have been generally provided with a precast bridge plug consisting essentially of sulphur. This sulphur plug is sealed into position by superimposing a layer of viscous waterproofing material such as pitch, which in turn is surmounted by a cast-in-situ layer of material similar in composition to the bridge plug itself. This mode of operation entails many disadvantages, and in addition necessitates the use of an inordinately long detonator case. This prior art method is also characterized by breakage of a large percentage of the bridge plugs because of their brittle nature. The exposure of detonators, sealed in the conventional manner with pitch and sulphur, to thermal changes occasionally results in channeling in the pitch, thus rendering the seal less efiective.

Another expedient to which the workers in the art have resorted, is the utilization of a precast plug of certain thermoplastic resins and rubberlike materials which are readily deformable. Such a readily deformable plug, however, offers insufiicient resistance to displacement of the embedded lead wires to assure that, under strain, they may not be moved relative (axially or radially) to the other components of the bridge plug assembly.

The object of the present invention is, therefore, to provide an electric blasting cap assembly, wherein the mouth of the casing is not only effectively sealed, but mechanically rugged.

Another object of the invention is to provide a method of manufacturing electric blasting cap closures wherein the susceptibility to malformation is minimized.

A more specific object of this invention is to provide a bridge plug for an electric detonator, so shaped as to prevent the detonator case from coming into dangerous proximit of the wires within the plug. These and other objects will become apparent as the invention is hereinafter disclosed.

Generally speaking, the objects of the invention. are accomplished by molding a circumferentially grooved plug of rigid dielectric material about the lead wires. With the circumferential groove filled with semi-solid sealing material, it is inserted into the mouth of a charged metallic case, and the latter is circumferentially crimped into the plug groove. The invention especially contemplates that the crimping of the case be limited, so that the crimp in the case is not contiguous with the bottom of the plug groove. This separation assures the maintenance of a ring of the semi-solid sealing material, which remains mobile, i. e., fiowable for long periods oftime.

The rigid plug is preferably composed of polystyrene, but may be made of any resinous synthetic material which is not deformable by the mechanical force required to crimp the case, or by the mechanical abuses to which the cap may be subject. The material must be a dielectric, and be capable of being molded around the usual lead wires to form waterproof seals.

It is preferable to in-cast the grooves as the plugs are molded, so that the part of the die forming the innermost portion of the groove prevents the lead wires from migrating toward the periphery of the plug, hence the possibility of the metallic case being crimped into contact with the lead wires is avoided.

References are made to the accompanying drawing, in order to describe the invention more clearly by means of specific embodiment:

Figure 1 is a perspective view of one embodiment of the bridge plug of this invention;

Figure 2 is a vertical View in cross-section of a complete assembly of an electric blasting cap which is provided with a bridge plug of Figure 1;

Figure 3 is a sectional View taken along line 33 of Figure 2; and

Figure 4 is a vertical cross-sectional view corresponding to Figure 2, but showing another form of bridge plug within the scope of this inven tion.

The blasting cap consists of the usual components, including: metallic case I containing the usual explosive charges 2; a bridge wire 3 connected between lead wires 4, having insulation 5; and a closure plug 6.

The lead wires 4 have molded thereabout in waterproof relationship, the plug 5 consisting preferably of a polystyrene composition. The upper portion of said lead wires within the plug is covered by the insulation material 5. The insulation material may be any of the common ones, such as fibrous cotton or a ncniibrous plastic such as ethyl cellulose or nylon. The lead wires in the interior of the plug follow a tortuous path, and their surfaces may be serrated or knurled to deviate from a straight line path or treated in any other manner, which will serve to assist the mechanical anchorage of these wires in the plug. The plug as shown has two circumferential grooves 8 about its periphery, but this number may be varied as desired. As shown in Figures 1 and 2, the grooves 8 are provided with inwardly extended depressions 9.

The plug 6 is prepared for insertion into a metallic case I by filling the circumferential grooves 8 and 9 with a neoprene putty composition, containing a plasticizer for polystyrene which assures that the putty will wet the polystyrene plug 6. Examples of suitable plasticizers are butyl oleate, normal butyl stearate, dibutyl phthalate and diethyl phthalate. The plug thus provided with the neoprene putty in the circumferential grooves is inserted into the mouth of the loaded case I and the latter is circumferentially crimped adjacent the grooves 8 as shown at 1. The crimping is such that the metal of case I is driven into contact with the banks l of the grooves 8. Where two such grooves are employed, the contact may be confined to the upper bank of one groove, and the lower bank of the other, but it is preferable and in fact easier to drive the metal into contact with both banks of a groove. By thus driving the crimp into contact at the banks of the groove 8, the plug 6 is anchored against axial displacement in the case I. The invention contemplates, however, that the crimp not be driven into contact with the bottom of the groove, else the putty will be eliminated. The spaced relation between the inner crest of the crimp and the bottom of the groove is readily achievable by a crimping tool whose edge is more blunt than the contour of the groove. Provision of the narrow extension 8 in the groove also insures against complete elimination of the sealing material, which is semi-solid and of a character which remains mobile for long periods of time, providing an effective seal under all conditions, and is so disposed that no mechanical strain can be imposed upon it.

In the crimping operation, some of the putty is driven out of the grooves 3 and exudes into the interspace between the plug 6 and the case I where, due to the thin section, it sets. Since both the metal case and the polystyrene plug are wettable by the neoprene putty, the resultant adhesion insures against relative twisting of the plug within the case.

in Figure 4, another form is shown wherein the circumferential grooves in the plug are of different contour, In this form the grooves It .are V-shaped, and the cooperating crimp l! is truncated so as to ventrap the annulus of mobile sealing material 9. The depicted plugs by no means exhaust the various types of grooves within this invention, but any and all shapes of grooves which could be molded into the plug and which would prevent the lead wires from attaining too close proximity to the portions of the groove which will ultimately contact the metallic case, and which would also serve as an annular pocket :forentrapping a ring of the sealing material, are contemplated by this invention.

It has been found that neoprene putty is particularly well suited as the sealing material to be positioned in the grooves of the plug, but any material which will remain in the grooves, preventing the passage of water or moisture, which does not become inoperative upon storage, and

which is thermally stable at temperatures, for instance, 0 C. to 50 C., to which detonators may be normally subjected in storage or handling, is suitable in this capacity. Thus, in place of the neoprene putty we may use thiokol, or any material which wets both case and plug, which has high viscosity and which in sections of 0.010 inch or more remains mobile at all temperatures to which detonators are subjected in normal handling and storage.

In the molding of detonator bridge plugs about leg wires, there is a tendency for the wires to migrate toward the periphery of the mold where they might ultimately make contact with the metallic case. This tendency is overcome when the grooves are ineast as the plugs are being molded. Internally projecting ridges on the mold which form the groove, prevent migration of the wires outwardly beyond the bottom of the grooves. Even if the lead wires are exposed in the very bottom of the groove, no electrical contact with the metallic case is possible when, as intended, a ring of dielectric sealing material is maintained between the crimp and the bottom of the groove.

The present invention thus overcomes simultaneously two of the most serious handicaps of the prior art electric blasting caps. The invention provides at once a simple and eflective means to prevent the entrance of water and moisture into electric blasting caps, a mechanically strong anchorage, and a radial reinforcement for the mouth of the case. The inven" tion also provides the art with an exceedingly simple and efiicient means and method for the electrical separation of the leg wires in the bridge plug and the detonator case.

Having thus described the invention, what is claimed and desired to be secured by Letters Paten 1s:

A device of the kind described comprising, a rigid plug embedding a pair of lead wires, said plug having a circumferential groove, a metallic case embracing .the grooved area of the plug, said case being crimped into contact with the banks of the groove but spaced from the bottom of the groove, and an annulus of neoprene putty confined between the crest of the crimp and the bottom of the groove.

ALDO J. BAROC'CA. FREDERICK R SEA-VEY.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 60,569 Schafiner Dec. 18, 1866 2,014,441 Matthews Sept. 17, 1935 2,356,337 Miller Aug. 22, 1944 2,428,884 Lefren Oct. 14, 1947 2,478,415 Mil1e1' Aug. 9, 1949 FOREIGN PATENTS Number Country Date 1 5,222 Great Britain of 1905 246,727 Great Britain Feb. 4, 1926 116,504 Germany June 13, 1899 161,542 Germany Oct. 20, 1903 

